1. Technical Field of the Invention
The present invention relates generally to a collision avoidance control system which works to initiate collision avoidance action when the danger of possible collision with a target present ahead of a vehicle is encountered.
2. Background Art
Automotive collision monitor systems are known which work to estimate stopping distances of a system-equipped vehicle and a target preceding vehicle traveling ahead of the system-equipped vehicle and locations of the system-equipped vehicle and the target preceding vehicle after the elapse of a preset time to determine the danger of possible collision with the target preceding vehicle based on the stopping distances and the locations. For instance, Japanese Patent First Publication No. 08-132996 teaches such estimation of the stopping distances. Japanese Patent First Publication No. 05-181529 (corresponding to U.S. Pat. No. 5,473,538) teaches such estimation of locations of the system-equipped vehicle and the target preceding vehicle.
It is, however, impossible for the above systems to determine the degree of deceleration to be produced in an automatic braking device of the system vehicle to avoid collision with the preceding vehicle based on the determination of the danger of possible collision. The systems, thus, need to perform an additional operation to determine a control variable to decelerate the system-equipped vehicle.
Japanese Patent First Publication No. 11-066495 teaches a collision avoidance control system which uses an intervehicle distance between the system-equipped vehicle and the target preceding vehicle, a relative speed between the system-equipped vehicle and the target preceding vehicle, a minimum distance to be reserved between the system-equipped vehicle and the target preceding vehicle, acceleration of the target preceding vehicle, and a preset deceleration of the system-equipped vehicle to derive a quadratic function in terms of conditions required to avoid accidental collision with the target preceding vehicle and determines the possibility of the collision using a parabola, as represented by the quadratic function. Specifically, this system increases the preset deceleration of the system-equipped vehicle cyclically and determines the possibility of the collision based on the orientation of the parabola, an inclination of a straight segment of the parabola, coordinates of the straight segment of the parabola, and a predefined parabola determining equation in each cycle to bring a target deceleration used in deceleration control into agreement with a value of the preset deceleration when it is determined that there is almost no possibility of the collision.
The system, however, has the drawback in that many mathematical operations are needed to determine the possibility of collision, thus resulting in a control lag.
The system also has an additional drawback in that when a range within which the preset deceleration is changed is fixed, it causes an operation load on the system to increase with a decrease in cyclic change in the preset deceleration, thus resulting in the need for limiting the magnitude of the cyclic change in the preset deceleration. Specifically, it is difficult to determine the target deceleration as a continuously changing value, thus resulting in a difficulty in improving the accuracy of the deceleration control.